Cancer research
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Cyclin-dependent kinase inhibitors (CKIs) p21, p27, p16, and p15 are an essential and integral part of cell cycle regulation. Studies on the expression of these inhibitors in normal versus tumor human breast cancer cells revealed that although p27 and p16 are expressed at higher levels in tumor cells, p21 and p15 expression were higher in normal cells. Analysis on the expression pattern of these proteins throughout the cell cycle in synchronized cells demonstrated a substantial increase in p21 during the S-phase in normal cells and barely detectable expression of p21 in any phase of the tumor cell cycle. ⋯ Synchronization of tumor cells by lovastatin, which arrests cells in G1, resulted in increased levels of p21 and p27 with a concomitant decrease in cyclin-dependent kinase 2-associated kinase activity. Synchronization of cells by double-thymidine block did not result in the induction of p21 or p27. These observations suggest that lovastatin causes a profound cell cycle-independent alteration of CKI expression which is distinct from growth factor deprivation or thymidine block.
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Analysis of MAGE-3-specific cytolytic T lymphocytes in human leukocyte antigen-A2 melanoma patients.
The MAGE-3 gene is a member of a multigene family that is selectively expressed by subsets of different human tumor types, including malignant melanoma, but not by normal tissues except for testis and placenta. A cytolytic T lymphocyte (CTL)-defined MAGE-3 antigen, corresponding to the MAGE-3 peptide 271-279 associated with the human leukocyte antigen (HLA)-A2 molecule, has been recently identified using T lymphocytes from a normal individual stimulated in vitro with peptide-pulsed autologous antigen-presenting cells. Because MAGE-3 is expressed in 76% of metastatic melanomas, the HLA-A2-restricted MAGE-3 antigen should be expressed by approximately 37% of Caucasians bearing a metastatic melanoma tumor, thus representing an attractive candidate for the elicitation of specific CTL immune responses in vivo. ⋯ In contrast, HLA-A1-positive melanoma lines transfected with MAGE-3 were efficiently recognized by CTL lines directed against the MAGE-3 peptide 168-176, a known HLA-A1-restricted CTL epitope. These results suggest that the expression level of the MAGE-3 peptide 271-279, unlike that of MAGE-3 peptide 168-176, in melanomas may be too low to allow efficient recognition by specific CTLs. Thus, it appears that despite the presence of CTL precursors against MAGE-3 peptide 271-279 in some HLA-A2+ melanoma patients, the usefulness of this peptide for specific immunotherapy of melanoma may be limited.